1. Field of the Invention
This invention relates to photopolymerizable photosensitive compositions which comprise, as main components, photopolymerizable photosensitive resins having ethylenically unsaturated groups of the specific type in the side chains or end groups thereof, and photopolymerization initiators. More particularly, it relates to photosensitive compositions which comprise novel resins of high sensitivity.
2. Description of the Prior Art
Photopolymerizable photosensitive compositions have now been used in the printing industry as photosensitive resin plates for relief printing and offset PS (presensitized) plates. In particular, the offset PS plates are much simpler in handling than known wipe-on plates, contributing to save the steps of the printing plate-making process. Accordingly, the PS plates have recently become popular more and more and are extending their market rapidly. Most of currently sold PS plates make use of so-called diazo-type photosensitive materials typical of which is a condensation product of paradiazodiphenylamine and formaldehyde. The PS plates using this type of diazo compound have relatively good sensitivity but are disadvantageous in that they are poor in printing durability, chemical resistance, and storage stability. In contrast, compositions comprising photo-crosslinkable photosensitive resins are able to form network molecular bonds therein upon irradiation of light, giving a printing plate of good printing durability. However, the compositions have the drawback that, in most cases, organic solvents are used as a developer to remove the photosensitive resin composition in non-crosslinked areas, thus being unfavorable from the standpoint of working environment and that the running cost becomes high. In contrast, with compositions comprising photopolymerizable photosensitive resins, the development is feasible with use of aqueous solutions and particularly aqueous alkali solutions. The aqueous solutions are more inexpensive than organic solvents coupled with another advantage in that they are less dangerous particularly from the physiological standpoint. In addition, the photopolymerizable photosensitive resin compositions form a molecular structure of three-dimensional network in portions where exposed, so that the resulting printing plate is very advantageous from the standpoint of printing durability.
Other important fields of applications of photo-crosslinkable and photopolymerizable photosensitive resin compositions include plating materials for metal corrosion at the time of fabrication of printed circuits, mask or resist materials for soldering processes, resist materials for chemical milling of metals, and resist materials used for fabrication of multi-layer metallic lithographs and gravure plates. For instance, in the fabrication of printed circuits, a substrate for the circuit, e.g. a copper substrate, is covered with a photosensitive resin composition on the surface thereof and exposed to light in an imagewise pattern, after which non-exposed areas are completely removed by the use of a suitable liquid developer while leaving a substantial area of the substrate to be exposed to air. The portions from which the photosensitive resin composition has been removed are etched by any known technique or plated with a metal. In these fields of applications, an aqueous alkali solution which is less dangerous can be used as a liquid developer, and photopolymerizable photosensitive compositions from which a durable resist film can be obtained are very advantageous.
In the above-mentioned various fields, a new image exposure system is being introduced in order to improve the working efficiency. For example, in case where an image is formed on an offset PS plate or a substrate for printed circuit, it is the common practice to bring an original film into intimate contact with the PS plate or substrate under which light is irradiated on the photosensitive layer of the plate or substrate through the film. In particular, with some offset PS plates, a system of exposure of the plate by an enlarged projection through a microfilm has been put into practice. This system has the advantage over known systems in that silver halide films can be saved. Also, another system is put into practice in which visible light from a laser beam, e.g. an argon ion laser beam, is directly scanned or exposed on a photosensitive layer of the substrate, thereby forming an image. This system does not need fabrication of silver halide films at all, so that much labor can be saved. Moreover, a further advancement of computerization will permit direct retrieval of signals of an image original from a computer. Thus, this type of laser exposure system is believed to be promising. However, in order to effectively form an image using the above-discussed new exposure systems, photosensitive resin compositions which are covered on individual substrates are required to have higher photosensitivity. It is generally accepted that photopolymerizable photosensitive resin compositions are superior to diazo photosensitive materials and photocrosslinkable photosensitive resin compositions. However, the above requirement is not adequately satisfied.
Accordingly, an object of the present invention is to provide compositions comprising photopolymerizable resins which can be developed by the use of aqueous alkali solutions and have higher speed of photosensitivity.
Known photopolymerizable photosensitive resins are, for example: products obtained by addition reaction of glycidyl (meth-)acrylates with polymers having carboxyl groups in the side chains thereof such as, for example, (co-)polymers (meaning the same as resins) of (meth-)acrylic acid, maleic acid and the like; products obtained by addition reaction of (meth-)acrylic acid with polymers having epoxy groups in the side chains such as, for example, glycidyl (meth-)acrylate (co-)polymers or epoxy-novolak resins; products obtained by reaction of (meth-)acrylic chloride with polymers having hydroxyl groups in the side chains thereof such as, for example, hydroxyethyl (meth-)acrylate (co-)polymers, vinyl alcohol and the like thereby introducing (meth-)acryloyl groups thereinto; and products obtained by reaction between polyurethanes obtained by polycondensation of polyols and diisocyanates, and (meth-)acrylates having hydroxyl groups. Thus, polymers having monofunctional ethylenically unsaturated groups in the side chains thereof are conventionally used.
The increase in amount of the ethylenically unsaturated compound in the composition containing photopolymerizable photosensitive resin usually results in an increase of the sensitivity.
However, ethylenically unsaturated compounds are ordinarily viscous liquids at a normal temperature. If the compound is added in an amount sufficient to obtain a desired level of sensitivity, the photosensitive layer becomes fairly adhesive on the surface thereof, making the handling very difficult.